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1		-#includeMacros("Main.MacroSheet")
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3		-1 #respect() Overview
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	5	+= #respect() Overview =
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5		-#respect() (*Re*action *Spec*ification *T*uples) is a logic-based language for the coordination of complex software systems.
	7	+#respect() (**Re**action **Spec**ification **T**uples) is a logic-based language for the coordination of complex software systems.
6	6	##
7	7	#respect() promotes a coordination model providing tuple centres as programmable, general-purpose coordination media.
8	8	##
9	9	The behaviour of #respect() tuple centres is programmed through the #respect() first-order logic language.
10	10
11		-1.1 The #respect() Tuple Centre Coordination Model
	13	+== The #respect() Tuple Centre Coordination Model ==
12	12
13	13	A tuple centre is a tuple space enhanced with the possibility to program its behaviour in response to interactions.
14	14	##
15		-First of all, coordinated entities (~~#respect() agents~~, henceforth, or simply ~~agents~~) can operate on a #respect() tuple centre in the same way as on a standard Linda tuple space: by exchanging ~~tuples~~ — which are ordered collection of knowledge chunks — through a simple set of coordination primitive.
	17	+First of all, coordinated entities (//#respect() agents//, henceforth, or simply //agents//) can operate on a #respect() tuple centre in the same way as on a standard Linda tuple space: by exchanging //tuples// — which are ordered collection of knowledge chunks — through a simple set of coordination primitive.
16	16	##
17	17	So, an agent can write a tuple in a tuple centre with an #code("out") primitive; or read a tuple from a tuple centre with primitives such as #code("in"), #code("rd"), #code("inp"), #code("rdp") specifying a tuple template - that is, an identifier for a set of tuples, according to some tuple matching mechanism.
18	18	##
19	19	Reading tuples can be
20		-* ~~destructive~~ — #code("in"), #code("inp") remove the matching tuple — or ~~non-destructive~~ — #code("rd"), #code("rdp") simply read the matching tuple
21		-* ~~suspensive~~ — #code("in"), #code("rd") wait until a matching tuple is found — or ~~non-suspensive~~ — #code("inp"), #code("rdp") immediately return either the matching tuple or a failure result
22		-but is anyway always ~~non-deterministic~~: when more than one tuple in a tuple centre are found that match a tuple template, one is non-deterministically chosen among them and returned.
23		-
	22	+* //destructive// — #code("in"), #code("inp") remove the matching tuple — or //non-destructive// — #code("rd"), #code("rdp") simply read the matching tuple
	23	+* //suspensive// — #code("in"), #code("rd") wait until a matching tuple is found — or //non-suspensive// — #code("inp"), #code("rdp") immediately return either the matching tuple or a failure result
	24	+<p/>
	25	+but is anyway always //non-deterministic//: when more than one tuple in a tuple centre are found that match a tuple template, one is non-deterministically chosen among them and returned.
	26	+<p/>
24	24	Accordingly, a tuple centre enjoys all the many features of a tuple space, which can be classified along three different dimensions:
	28	+
25	25	* generative communication
26	26	* associative access
27	27	* suspensive semantics
28		-
29		-The main features of ~~generative communication~~ (where information generated has an independent life with respect to the generator) are the forms of uncoupling (space, time, name) based on mediated interaction: sender and receiver do not need to know each other, to coexist in the same space or at the same time in order to communicate (to exchange a tuple, in particular), and more generally, to interact.
	32	+<p/>
	33	+The main features of //generative communication// (where information generated has an independent life with respect to the generator) are the forms of uncoupling (space, time, name) based on mediated interaction: sender and receiver do not need to know each other, to coexist in the same space or at the same time in order to communicate (to exchange a tuple, in particular), and more generally, to interact.
30	30	##
31		-~~Associative access~~ (access based on structure and content of information exchanged, rather than on location, or on name) based on tuple matching promotes synchronisation based on tuple structure and content: thus, coordination is data-driven, and allows for knowledge-based coordination patterns.
	35	+//Associative access// (access based on structure and content of information exchanged, rather than on location, or on name) based on tuple matching promotes synchronisation based on tuple structure and content: thus, coordination is data-driven, and allows for knowledge-based coordination patterns.
32	32	##
33		-Finally, ~~suspensive semantics~~ promotes coordination patterns based on knowledge availability, and couples well with incomplete, partial knowledge.
34		-
35		-Even more, while the basic tuple centre model is independent of the type of tuple, #respect() tuple centres adopt logic tuples &mdash; both tuples and tuple templates are essentially Prolog ~~facts~~ &mdash; and logic ~~unification~~ is used as the tuple-matching mechanism.
	37	+Finally, //suspensive semantics// promotes coordination patterns based on knowledge availability, and couples well with incomplete, partial knowledge.
	38	+<p/>
	39	+Even more, while the basic tuple centre model is independent of the type of tuple, #respect() tuple centres adopt logic tuples &mdash; both tuples and tuple templates are essentially Prolog //facts// &mdash; and logic //unification// is used as the tuple-matching mechanism.
36	36	##
37	37	So, for instance, an agent #code("ag1") performing operation #code("we ? in(activity(ag1,CaseID))") on tuple centre #code("we") containing tuples #code("activity(ag1,c16)") and #code("activity(ag2,c22)") will be returned tuple #code("activity(ag1,c16)") &mdash; the one unifying with the template &mdash; removed from #code("we").
38	38	##
39		-Since the overall content of a tuple centre is a multiset of logic facts, it has a twofold interpretation as either a collection of messages, or a (logic) ~~theory of communication~~ among agents &mdash; thus promoting in principle forms of ~~reasoning about communication~~.
40		-
41		-Finally, a tuple centre is a programmable tuple space, so as to add ~~programmability~~ of the coordination medium as a new dimension of coordination.
	43	+Since the overall content of a tuple centre is a multiset of logic facts, it has a twofold interpretation as either a collection of messages, or a (logic) //theory of communication// among agents &mdash; thus promoting in principle forms of //reasoning about communication//.
	44	+<p/>
	45	+Finally, a tuple centre is a programmable tuple space, so as to add //programmability// of the coordination medium as a new dimension of coordination.
42	42	##
43	43	While the behaviour of a tuple space in response to interaction events is fixed &mdash; so, the effects of coordination primitives is fixed &mdash;, the behaviour of a tuple centre can be tailored to the system needs by defining a set of specification tuples, or reactions, which determine how a tuple centre should react to incoming / outgoing events.
44	44	##
45	45	While the basic tuple centre model is not bound to any specific language to define reactions, #respect() tuple centres are obviously programmed through the #respect() logic-based specification language.
46	46
47		-1.1 #respect() as a Core Coordination Language
	51	+== #respect() as a Core Coordination Language ==
48	48
49	49	The original #respect() is a logic-based language for the specification of the behaviour of tuple centre.
50	50	##
51	51	As a behaviour specification language, #respect():
52	52
	57	+
53	53	* enables the definition of computations within a tuple centre, called reactions, and
54	54	* makes it possible to associate reactions to events occurring in a tuple centre.
55		-
	60	+<p/>
56	56	So, #respect() has both a declarative and a procedural part.
57	57	##
58	58	As a specification language, it allows events to be declaratively associated to reactions by means of specific logic tuples, called specification tuples, whose form is #code("reaction(E,R)").
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64	64	A reaction as a whole succeeds if all its reaction goals succeed, and fails otherwise.
65	65	##
66	66	Each reaction is executed sequentially with a transactional semantics: so, a failed reaction has no effect on the state of a logic tuple centre.
67		-
	72	+<p/>
68	68	All the reactions triggered by an event are executed before serving any other event: so, agents perceive the result of serving the event and executing all the associated reactions altogether as a single transition of the tuple centre state.
69	69	##
70	70	As a result, the effect of a coordination primitive on a logic tuple centre can be made as complex as needed by the coordination requirements of a system.
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72	72	Generally speaking, since #respect() has been shown to be Turing-equivalent, any computable coordination law could be in principle encapsulated into a #respect() tuple centre.
73	73	##
74	74	This is why #respect() can be assumed as a general-purpose core language for coordination: a language that could then be used to represent and enact policies and rules for coordination systems of any sort.
75		-
76		-Adopting the declarative interpretation of logic tuples, a #respect() tuple centre has then a twofold nature a ~~theory of communication~~ (the set of the ordinary tuples) and a ~~theory of coordination~~ (the set of the specification tuples).
	80	+<p/>
	81	+Adopting the declarative interpretation of logic tuples, a #respect() tuple centre has then a twofold nature a //theory of communication// (the set of the ordinary tuples) and a //theory of coordination// (the set of the specification tuples).
77	77	##
78	78	In principle, this allows intelligent agents to reason about the state of collaboration activities, and to possibly affect their dynamics.
79	79	##
80	80	Furthermore, the twofold interpretation (either declarative or procedural) of #respect() specification tuples allows knowledge and control to be represented uniformly (as Prolog-like facts) and encapsulated within the same coordination artefact.
81	81
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